Method of forming semiconducting materials and barriers using a dual enclosure apparatus

ABSTRACT

In a gaseous glow-discharge process for coating a substrate with semiconductor material, a variable electric field in the region of the substrate and the pressure of the gaseous material are controlled to produce a uniform coating having useful semiconducting properties. Electrodes having concave and cylindrical configurations are used to produce a spacially varying electric field. Twin electrodes are used to enable the use of an AC power supply and collect a substantial part of the coating on the substrate. Solid semiconductor material is evaporated and sputtered into the glow discharge to control the discharge and improve the coating. Schottky barrier and solar cell structures are fabricated from the semiconductor coating. Activated nitrogen species is used to increase the barrier height of Schottky barriers.

This is a division of application Ser. No. 07/394,287 filed Aug. 16,1989, now U.S. Pat. No. 5,049,523, which is a continuation ofapplication Ser. No. 07/180,720, filed Apr. 4, 1988 now abandoned, whichis a continuation of application Ser. No. 06/935,606, filed Dec. 1, 1986now abandoned, which is a continuation of application Ser. No.06/716,409, filed Mar. 27, 1985 now abandoned, which is a division ofapplication Ser. No. 06/355,202, filed Mar. 5, 1982, now abandoned,which is a division of application Ser. No. 06/088,100, filed Oct. 24,1979 now U.S. Pat. No. 4,328,258, which is a division of applicationSer. No. 05/857,690, filed Dec. 5, 1977 now U.S. Pat. No. 4,226,897.

BACKGROUND OF THE INVENTION

Hydrogenated amorphous silicon films, hereinafter called a-Si, which aresuitable for semiconductor applications have been prepared by a varietyof techniques. Chittick, Alexander, and Sterling reported in the Journalof the Electrochemical Society, vol. 116, No. 1 (Jan. 1969) pages 77-81,in an article entitled "The Preparation and Properties of AmorphousSilicon", that an inductively coupled, RF glow-discharge in silane(SiH₄) gas produced low-conductivity a-Si films that could be doped withboth donor and acceptor impurities, thereby changing the a-Siconductivity over a wide range of values. More recently, a-Si films wereproduced by evaporating silicon in an atmosphere of hydrogen (H₂) and bysputtering silicon in an atmosphere of H₂ +Ar which exhibited similarsemiconductor characteristics to those films made from silane in aglow-discharge.

Presently, several commercial projects related to the development ofSchottky barrier solar cells using crystal, polycrystal, and amorphoussemiconductor materials were described in a recent book entitled TwelfthIEEE Photovoltaic Specialists Conference 1976, published by theInstitute of Electronic and Electrical Engineers Inc., New York, N.Y.,10017. On pages 893-895 of this book, Carlson et al. reported in anarticle entitled "Solar Cells Using Schottky Barriers on AmorphousSilicon" that he formed a solar cell by applying a transparent electrodewith appropriate work-function to one side of an a-Si film and an ohmiccontact to the other. Also, this article stated output voltagesincreased initially by 100 mV when the thin metal electrode wasevaporated in residual oxygen background in the vacuum system, producinga metal-insulator-semiconductor (MIS) structure. More recently, Carlsonreported in vol. 77-2 Extended Abstracts, Fall Meeting, Atlanta, Ga.,Oct. 9-14 1977 of the Electrochemical Society, Princeton, N.J. 08540,pages 791-792, that these MIS cells were generally unstable.Furthermore, Carlson reported that his electrodes were less than 0.02cm² in area--a value too small for commercial use. Also, an article byGodfrey and Green in Applied Physics Letters vol. 31, No. 10, (Nov. 15,1977) pages 705-707, indicates that such small areas lead to erroneousdata.

My prior glow-discharge coating processes are covered in U.S. Pat. Nos.3,068,283, 3,068,510 (Dec. 18, 1962) and U.S. Pat. No. 3,600,122 (Aug.17, 1971). These processes generally related to polymeric coatings whichhave resistivities greater than 10¹² ohm-cm High-resistivity coatingsact as blocking capacitance in series with the glow-discharge therebyassisting in regulation of coating uniformity. However, neither 60 Hzline transformers nor DC power supplies can be used with my priorprocesses. The present process, on the other hand, producesemiconducting films which act primarily as resistances in series withthe glow discharge and which require different process concepts.

SUMMARY OF THE INVENTION

The present coating process is related to producing semiconductor filmswhich have electrical resistivities generally less than about 10¹²ohm-cm at room-temperature, and preferably between 10¹² and 10⁶ ohm-cm.The present process is designed to produce uniform semiconductingcoating over a large area by means of a glow-discharge in which pressureand electric field are controlled. Also, the present process relates tothe treatment of a semiconductor surface to increase the Schottkybarrier voltage when an active conducting coating is applied. Suchtreatment may be used on any semiconductor material, including crystalsemiconductors which have conductivities of 100 and 0.01 ohm cm. andhigher. My coating process and barrier treatment is particularly usefulfor producing a Schottky barrier solar cell.

The principle object of the process is to produce a semiconductor andbarrier for use in a solar cell. Another object of the invention is tocoat a large-area substrate with amorphous semiconducting material. Yetanother object is to form a Schottky barrier between a semiconductingmaterial and an active electrode. Another object is to dope large areaamorphous semiconductor materials to form an ohmic contact with aconducting substrate. Another object is to introduce semiconductormaterial form a solid-source into a coating being formed byglow-discharge deposition form the gas-phase.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a cross-sectional view of apparatus illustratingglow-discharge in the weak electric field.

FIG. 2 is a cross-sectional view of devices using semiconductor materialproduced in a glow-discharge and treated with activated nitrogen.

FIG. 3 illustrates another embodiment of the invention in which multipleelectrodes are employed to maintain a glow-discharge.

FIG. 4 illustrates another embodiment in which the substrate is movedthrough the glow-discharge.

FIG. 5 illustrates another embodiment in which the electric fieldconfiguration and pressure are adjusted to enable alternating voltagesto be applied while collecting a substantial part of the semiconductingmaterial.

FIG. 6 illustrates another embodiment in which semiconductor material isevaporated through the glow-discharge to stabilize the discharge andattain desired semiconducting properties.

FIG. 7 illustrates another embodiment in which semiconductor material issputtered through the glow-discharge to stabilize the discharge andattain desired semiconductor properties.

DESCRIPTION OF THE APPARATUS AND TECHNIQUES

Referring to FIG. 1 and FIG. 2a, cross-sectional views are illustratedof the glow-discharge apparatus and a typical device made therein. Thesubstrate 1 is a 0.010" thick stainless-steel plate 11 with rectangulardimensions of 3"×4" supported by electrode 2. Resistance heater 3 isembedded in ceramic block 3a which supports and heats electrodes 2, 11.Substrate 1 is positioned in the open face of concave counter electrode4 which has a rectangular cross-section of 4"×5" defined by side-walls 8and top 9. Top 9 is positioned at least 41/2" above the front surface ofsubstrate 11. Electrode assemblies 1 and 4 are positioned inside anenclosure 6 and header 12 and are joined by appropriate gasket to form agastight seal. Vacuum pump 20 is connected through valve and nipple 13to header 12 to evacuate enclosure 6. Gases G from tanks 17 a-e areconducted through regulated needle valves 16 a-e, manifold line 15, andconnector 14 through header 12 into enclosure 6. Here, gases G areconducted through dielectric tubing 5 and diffusor 7 inside electrode 4.A gap 118 of say 1/2" between walls 8 and electrode 2 permits egress ofgases G after passing through glow-discharge P. Gauge VG meters theevaluation of enclosure 6 and pressure of gases G. Gauge VG ispreferably of the capacitance-manometer type which is commerciallyavailable for use with corrosive, condensible gases, in the range of0.001 to 10 Torr. Readings from Gauge VG may automatically regulatevalves 16 through a servo-mechanism to maintain a desired pressure. Apotential V is applied between electrodes 2, 4 from power supply 24 byleads 21, 22 connected through insulated electrical bushings 18, 19sealed in header 12. Protective network 23 prevents damaging sparks.Voltage V and current I are metered as indicated. Resistance heater 3enclosed in ceramic 3a is connected through leads 45 and electricalbushings 45' to an appropriate power source (not shown).

In operation, the enclosure 6 is evacuated by pump 20 to a pressurebelow about 0.02 Torr and back-filled with silane (SiH₄) from tank 17aby opening valve 16a. Valve 16a is adjusted to maintain the desiredpressure in enclosure 6 which, for example, may be 1/2 Torr. Next amixture of 10% phosphine (PH₃) in helium (He) from tank 17b is admittedinto manifold 15 where it mixes with silane and flows through lines 5, 7to raise the system pressure PG to about 1 Torr. The potentialdifference V between electrodes 2, 4 is adjusted to about 530 voltsinitiating a glow-discharge and the current, I, adjusted to about 5 mAto produce a heavily doped n⁺ coating 101 on plate 100. Aftermaintaining the discharge for about 1 minute, valve 16b is closed toshut off the flow of PH₃ and He leaving silane alone. The uniformity andimpurity level of ohmic-layer 101 is not as critical as that of thehigh-resistivity a-Si layer 10. Therefore, ohmic-layer 101 may bedeposited by conventional doped chemical-vapor-deposition (CVD) or othertechniques, prior to insertion in the apparatus of FIG. 1.

Next, the pressure PG of silane is adjusted to 0.3 to 0.4 Torr toposition a diffuse discharge P in the region above plate 100 andminimize the discharge in the region of closest separation d betweenelectrodes 2, 4. The discharge then occurs in the weaker region of theelectric-field E as will be discussed in more detail in connection withFIG. 5b. The discharge is maintained for 40 minutes at 5 mA to 10 mA(0.1 to 0.2 mA cm²) with V in the range of 500-1500 depending on PG.After desired thickness on substrate 1 is attained, valve 16b is closedand the residual gases evacuated to background pump 20. Valve 16c onammonia (NH₃) tank 17c is opened to admit NH₃ into the substrate region1 to a pressure of about 400 Torr. A potential difference V is appliedbetween electrodes 2, 4 of about 350 volts and I of 5 mA to 10 mA toproduce a glow-discharge adjacent coated substrate 1. Valve 16c isclosed, the residual gases in enclosure 6 evacuated by pump 20, and theenclosure 6 is backfilled with nitrogen from tank 17d (valve 16d) topurge unreacted silane. Valve 13 is closed, jar 6 is raised toatmospheric pressure and substrate 1 removed.

Referring to FIG. 2a, the substrate 1 is illustrated with foil 100coated with n⁺ -doped a-Si layer 101, undoped 1-4 um a-Si layer 10 andammonia-treated layer 30. The substrate 1 is then placed in aconventional vacuum-evaporator and coated with a high work-function,semi-transparent metal 31 (such as palladium) to a thickness of about100 A or less to complete the Schottky barrier. The conducting layer 31is adjusted to be thick enough to reduce its sheet resistance while notabsorbing an inordinate amount of incident photons. A grid 32 of thickermetal such as a silver-titanium alloy (Ag--Ti) is applied to reduce theseries resistance of the semi-transparent electrode 31. Also, a topanti-reflection (AR) layer 33 such as Si₃ N₄ with a thickness range ofabout 1000 Å may be applied to electrode 31 to reduce reflection lossunder photon irradiation. Under test using AM1 illumination and aTektronix Corp. curve tracer, the short-circuit current Isc was measuredto be about 2 mA/cm² and the open-circuit voltage Voc was about 350 mV,with nc AR coating and 50% reflection loss. When the layer 30 was addedby the NH₃ discharge, Isc remained about 0.1 to 0.2 mA/cm² while the Vocwas measured to be greater than 600 mV--an increase in excess of 250 mV,again with no AR coating. Similar increases were found with othersubstrates as illustrated in the following drawings.

Referring to FIG. 2b, a glass substrate 104 coated with a transparentconducting coating 105 of the oxides of indium (In) and tin (Sn)(commercially available) may be inserted into the apparatus of FIG. 1 onelectrode 2 with the conducting coating 105 facing the discharge andconducting tab 106 contacting electrode 2. Thereafter, the coatingprocedure is the same as that described in connection with FIG. 2a, inthat ohmic contact layer, a-Si layer 40, NH₃ -treated barrier-layer 41are produced sequentially. Also, using an evaporator, a Pd coating 42 isapplied to complete the Schottky barrier and a thicker metallic layer 43such as Ti-Ag applied to complete the contact. When substrate 1 isilluminated (in operation) through the glass substrate 104, electrode 43may be opaque. An additional AR coating 107, such as an oxide oftantalum, may be applied to the glass. Although the glass substrate 104serves as a useful material, protective material, the configuration ofFIG. 2b produces somewhat less output than that of FIG. 2a since themaximum number of charge carriers are generated at the ohmic surfacewhere the incident photons impinge first rather than at the barrierwhere the output potential is developed.

Referring again to FIG. 2a, b, p-type a-Si may be substituted for then-type a-Si in coatings 10, 40 by doping with a donor impurity duringformation in the apparatus in FIG. 1. For example, during formation ofthe a-Si coating 10, the apparatus of FIG. 1 may be operated asdescribed above except that diborane from tank 17e (valve 16e) is addedto the silane flow from tank 17b to dope the a-Si layer 10 to neutral orto p-type depending on the fractional amount of B/Si. Correspondingly,1-10% diborane from tank 17e may be added to G to dope the ohmic-layer101 to p⁺ level. For p-type a-Si, the active metal layer 31 is formedfrom a low work-function metal such as chromium (Cr) or aluminum (Al).In either case the layer 101 may be formed by NH₃ -discharge to enhancethe Schottky barrier with any of the structures such as shown in FIG.2a, b, c.

Referring again to the apparatus of FIG. 1, I found that barrier-heightand Voc of an untreated a-Si material may be increased byglow-discharging in N₂ gas instead of NH₃. However, using the structureof FIG. 2a, when layer 30 was formed from a N₂ discharge the increase inVoc amounts to only about 100 mV instead of 250 mV with NH₃. Also,nitrogen atoms (N) produced an increased barrier. For example, using acommercial plasma torch producing a nitrogen atom beam to treat thesurface 10, Voc increased by 150 mV after 15 minutes treatment. Thisvalue is somewhat larger than the direct N₂ discharge but smaller thanthe 250 mV under direct NH₃ glow-discharge. Hydrazone proved moreeffective than N₂ alone. Air in an atomic beam was found to increase theVoc also; however, oxygen alone in a glow-discharge formed a blockinglayer. The discharge for producing the NH₃ treated layer 30 is not ascritical as that for producing the a-Si layer 10 since the gases, perse, do not form a film but combine with the coating 10, depositedpreviously. The glow-discharge time-limits are determined by thelimiting thickness through which charge carriers can tunnel.

Referring to FIG. 2c, the substrate 1 is 0.0035" thick stainless-steelfoil 102 reinforced with frame 109 which may be 1/16" or thicker, toprevent foil 102 from bending in a small radius and damaging the a-Sifilm 110. Again, a barrier layer 111 is formed by discharge treatment inammonia. However, an additional barrier layer 112 is added which may beantimony trioxide (Sb₂ O₃) or titanium dioxide (TiO₂) or other metallicoxides or nitrides having a thickness 50 Å or less to enhance thebarrier height without blocking the desired charge carriers. In the caseof TiO₂, the semi-transparent layer 36 may be nickel (Ni) with athickness 100 Å or less and may have an additional conducting layer of50 Å or so of chromium (not shown). Contact fingers 35 and AR coating 33are added to complete the photo-voltaic Schottky barrier. The cells ofFIG. 2a, b, c may be made with any semiconductor material having aphotoresponsive barrier such as that made in the following apparatus.

Referring to FIG. 3, the anode 4 of FIG. 1 is replaced by a set ofcylindrical pins 80 supported by a dielectric holder 81. Each pin 80 isconnected through protective resistors 82 to ⁺ V. The surfaces ofdielectric holder 81 and resistors 42 are positioned at least about 6"above the substrate 1 to advoid deposition of conducting siliconmaterial (M noted in FIG. 1). Typical operating conditions are similarto those described in connection with FIG. 1 in that the desired gases Gare admitted through a suitable distributor (not shown) and exhausted bya pump (not shown) except that the pressure and current density can beoperated at higher values say up to 2 Torr and 1 mA/cm² and higher.Also, substrate 1 can be moved through the discharge for continuouscoating or may remain static. Again, the fringing field lines E permitthe discharge to move up the pins 80 by adjustment of pressure whilemaintaining the discharge in the weaker field E_(w).

Other geometries can be used for pins 40 such as tapered pins or hollowcylinders facing the substrate 1. Silicon which is collected on the pins40 represents wasted material. However, I found that by applying DC orDC plus AC with the pins 40 biased anodically, silicon collection isminimized. For designing protective resistors 42, if the average currentdensities (I/area) to substrate 1 is adjusted to be 0.2 mA/cm² and withpins 40 1 cm apart, resistors may be in the range of 100 k ohms for goodregulation. Hollow pins are described with a moving substrate in FIG. 4.

Referring to FIG. 4, an in-line system is illustrated schematicallyusing hollow electrodes 70 with configuration similar to that in FIG. 3.A loading chamber 60, airlock 61, ohmic-layer deposition system 62, anda-Si deposition-system 63 produce continuously coated substrates 1 suchas those shown in FIGS. 2a, b, c. Finally, chamber 64 treats the coatedsubstrate with activated ammonia species to form the barrier-layer.Appropriate gases G1, G2, G3 are distributed through lines 75, 76, 77into ceramic chambers 78, 79, and 80 which may conveniently houseelectrodes 71, 72, 73 respectively. The gases from distributors 78, 79,80 flow through hollow pins 71, 72, 70 into pumping ports 65, 66 and areexhausted by pumps (not shown). Pressures in ports 65, 66 are adjustedto be below that in compartments 62, 63, 64 to insure that the exhaustgases G do not flow into adjacent compartments. In operation, the sizeof each compartment 62, 63 and 64 is adjusted for the dischargeresidence time to produce the desired coating thickness. Resistanceheaters 67, 68, 69 maintain the substrate 1 at the desired temperature.The temperature of the substrate 1 in the a-Si region 63 should bebetween 200° and 350° C., whereas the temperature in the ohmic-layerregion 62 can be considerably higher. The temperature in the NH₃ regionshould be below about 300° to advoid dehydrogenation of the a-Si.

In operation, airlock 61 is closed and the substrate 1 which, forexample, are one meter square stainless steel plates, are loaded inchamber 60 and the air is evacuated. Air lock 61 is opened and acommercial feeder mechanism (not shown) moves the substrate 1 alongguide-rail 48 which acts as the electrical connection to ground forsubstrate 1. Suitable mechanical mechanisms include individual movingarmatures, endless conveyor belts and ultrasonic walkers. Substrate 1 isunloaded and collected in a stacking mechanism not shown in compartment27. Air lock 68 is closed and coated substrates 1 moved to theevaporation system as described in connection with FIG. 1.Alternatively, loading and unloading compartments 60, 27 could bereplaced with continuous seals, which are standard in the vacuum coatingindustry, to provide vacuum to air operation. Other suitable electrodeconfigurations such as those described in FIG. 5 may be used with amoving substrate.

Referring to FIG. 5a, the preferred embodiment, electrodes areillustrated which enable the use of AC and efficient collection on thesubstrate 1 of a substantial part of the a-Si. Parallel, rectangularelectrodes 92, 93 hold stainless steel plates 90, 91 forming substrateassembly 1. End tabs 92a, 93a on electrodes 92, 93 insure goodelectrical contact to substrates 90, 91 and may act as guides ifsubstrates 90, 91 are moved during deposition. Electrical contact toelectrodes 92, 93 is made by leads 96, 97 having ceramic insulators 98,99. Leads 96, 97 are connected to center-tapped transformer 152. Theplates may be supported by leads 96, 97 and additional insulators (notshown). Electrodes 92 are heated, for simplification of theillustration, by resistance-heater 95, ceramic insulation 94, andsupported by a suitable ceramic rod 84. A small gap 88 is maintainedbetween heater insulation 94 and electrodes 92, 93 to advoidshort-circuiting electrodes 92, 93 through conducting Si, which depositson insulation 94. Also, dielectric members 98, 99, and 84 should extenda distance greater than about 6" from the region of electrodes 90, 91under glow-discharge. Input ases G are distributed and exhausted fromlines (not shown) as described in connection with FIG. 1.

In operation, silane gas G is admitted to a pressure of about 0.4 Torrand, when electrodes 92, 94 have a minimum separation of 1/2", a RMSvoltage of about 650 volts between electrodes 90, 91 from 60 Hztransformers 152 produces a current of 5 mA or about 0.2 mA/cm². Theseoperating values are similar to those used with the DC supply of FIG. 1,except that each plate 90, 91 becomes cathodic alternately. Asillustrated in FIG. 5b, the negative glow encircles plates 90, 91 in theweak electric field E_(w) and, for 1/2" separation d, a silane pressureof 0.35 Torr eliminates all glow-discharge in the strong field E_(s).The actual operating pressure of 0.40 Torr allows some discharge to theinactive ends. The pressure used during deposition of the ohmic-layerand NH₃ treatment is determined separately.

In practice, I found that transformer 152 of the neon-sign type wasconvenient for developmental-size models. In production, larger,self-regulating SCR, or saturable reactor transformers can be used. Linefrequencies (50-60 Hz) and audio frequencies to 20K Hz, which aresupplied from inexpensive solid state supplies, are the preferred powersources.

Referring to FIG. 6, an e-beam evaporation source 160 (commerciallyavailable) having an electron gun 50, magnetic deflector 51, andcrucible 52 with electric contact 53, is used to evaporate polycrystal(pxSi) 164 through a glow-discharge P onto substrate 1. Substrate 1 iscomprised of stainless steel plate 54 retained on electrode 55 andheater 56 in ceramic enclosure 57 as discussed in connection with FIG.1, however, electrodes 54, 55 are attached to arm 58 mounted on shaft59. Shaft 59 may be rotated by a conventional mechanism (not shown) tomove plate 54 from the coating region above source 160 to the vacuummetallization region (not shown) to apply electrodes as described inconnection with FIG. 2a, b, or the TiO₂ barrier layer, as described inconnection with FIG. 2c. Baffle plate 89 and a high-capacity blower-pump(not shown) permit a low pressure in the evaporator region 160 and ahigher pressure in the glow-discharge region P around substrate 1.

In operation, the crucible 56 may be grounded by lead 53 and a potential-V is applied to substrate 1 to maintain the glow-discharge P in gasesG. A negative potential -V may be applied to the e-beam source 50 tobombard and heat crucible 56, or other suitable heat sources may be usedto heat crucible 56 to evaporate silicon. Evaporated Si passes throughthe glow-discharge P where it is partially ionized and joins the silaneions to coat the surface of plate 56. The evaporated material stabilizesthe glow-discharge P and improves the semiconducting properties of thecoating on plate 55. Gases G may be doped, undoped, or NH₃ as discussedin connection with FIG. 1. However, additional doping may be appliedfrom the material in crucible 56. Also, any of the structuresillustrated in FIGS. 2a, b, c may be formed and ammonia may be addedwithout operating evaporation source 160.

Referring to FIG. 7, a sputtering source 89 of the inverted magnetrontype such as I described with E. G. Linder and E. G. Apgar inProceedings of the IRE (now IEEE) (Jul. 1952), pages 818-828. The source89 has a cylindrical electrode 85 composed of poly-crystal Si, endplates 87, anode ring 86, and magnetic field B with its principlecomponent longitudinal to the axis of the electrode 85. The substrate 1has plates 114, electrodes 115, heater dielectric 116 and element 17similar to substrate 1 described in connection with FIG. 1. Substrate 1is positioned to receive silicon sputtered from electrode 85. Apotential -V relative to ring 86 maintains a glow-discharge ininput-gases G in the vicinity of the surface of plate 114.

In operation, gases G10 such as Ar or Ar+H₂ are injected betweenmagnetron electrons 85, 86. A suitable potential, +V, on anode 86 andmagnetic-field B are maintained to sputter silicon onto the surface ofplate 114. At the same time, a potential -V is applied to substrate 1relating to electrode 85 to maintain a glow-discharge P in gases G10 andsputtered silicon from source 85. The potential -V is maintained untilthe ions in glow-discharge P deposit on substrate 114 to form a film ofthe desired thickness. Silicon from the sputter source 89 facilitatesmaintainance of a uniform glow-discharge in the vicinity of substrate 1and improves conductivity characteristics of Schottky barriers such asillustrated in FIG. 2a, b, c.

Although I have used for convenience silane gases in the illustrations,other silicon-hydrogen gases can be used such as SiHCl₃ and SiH₂ Cl₂.Also, other semiconductor gases such as germane can be used to formhydrogenated amorphous germanium. Non-hydrogenated semiconductors canalso be used with the present invention including the binary alloys ofgallium. For example, trimethylgallium gas glow-discharged with severalother gases forms semiconductor films: with arsene, forms GaAS; withNH₃, forms GaN; and, with Ph₃, forms GaP. Apparatus illustrating otherdevices utilizing such semiconductor films are shown in FIG. 5, and theother drawings.

Referring to FIG. 8, a solar thermal-collector is shown with a 1 um a-Sifilm 121 and a-Ge film 123 coated on the front of stainless-steel plate123 assembly which faces the solar radiation. Water 124, is circulatedby input tubing 125 and output tubing 126 through enclosure 127 where incontacts the rear of plate 123. Transparent glazing 127, such asplate-glass, and enclosure 128 holds and insulates plate assembly 124which is elevated in temperature by the solar radiation.

Under illumination, the visible solar radiation component which passesthrough glazing 12 is absorbed in the a-Si coating 121. The infra-red(IR) component of the solar radiation passes through the a-Si coating121 and is absorbed in the a-Ge coating 122. Plate 123, preferably, hasa polished or metallized surface with low IR emissivity for radiationwavelengths above say 2 um--which would otherwise be radiated from thesolar-heated plate 123, itself. Thus, the a-Si absorbs visible radiationwhereas a-Ge, which has a smaller band gap than a-Si, absorbs the IRcomponent. The a-Si, a-Ge films 121, 122 in combination yield close tothe ideal characteristics of a solar thermal-collector-high absortivityand low IR emissivity. Any of the processes described above may be usedto coat the a-Si and a-Ge layers 121, 122. Also, the coated plateassembly 123 may be used separately without glazing 129 and box 128 as aselective surface in a focused collector (not shown). It should be notedthat both a-Si and a-Ge formed in my apparatus absorb more efficientlythan crystal Si or Ge, and cost substantially less than crystals.Another application of films made with the process is shown in FIG. 9.

Referring to FIG. 9, a p-n junction is shown with a stainless steelsubstrate 131 coated with a-Si film 132 which has a heavily doped n⁺layer making ohmic-contact with plate 131 as described in connectionwith FIG. 1. A p (or pp+) layer 134 is added to coating 132 forming ap-n junction. Top Cr contact layer 135 may be semi-transparent, if thedevice of FIG. 9 is operated as a solar cell. Alternate substrate 131surfaces include alloys of antimony (Sb) and gold (Au).

Other applications of the coating process and the improved barrier-layerare field-effect-transistors (FET),insulated-gate-field-effect-transistors IGFET, andcharge-coupled-devices CCD.

I claim:
 1. The method of producing a semiconductor junction comprisingamorphous silicon on the surface of a substrate in an evacuatedenclosure comprising a first enclosure and a second enclosure, a firstmeans for introducing a first gaseous material comprising a dopant intosaid first enclosure, a second means for introducing a second gaseousmaterial comprising silicon and hydrogen into said second enclosure, ameans for restricting the flow of said dopant from said first enclosureinto said second enclosure, and a means for transporting said substratefrom said first enclosure through said flow-restricting means to saidsecond enclosure, a first electrode means for applying a first electricfield to said substrate in said first enclosure and a second electrodemeans for applying a second electric field to said substrate in saidsecond enclosure, which includes the steps of:introducing said first andsecond gaseous materials at subatmospheric pressures in said first andsecond enclosures, applying said first electric field by said firstelectrode means to said substrate in said first enclosures to deposit adoped film, transporting by said transport means said substrate throughsaid flow restricting means into said second enclosure, applying saidsecond electric field by said second electrode means to said substratein said second enclosure while controlling the pressure of said firstgaseous material comprising a dopant in said first enclosure and saidsecond gaseous material comprising silicon and hydrogen in said secondgaseous enclosure and restricting the flow by said flow-restrictingmeans of said first and second gaseous materials between said first andsecond enclosures to deposit a film comprising amorphous silicon in saidsecond enclosure substantially free of said dopant from said gaseousmaterial comprising a dopant in said first enclosure.
 2. The method ofproducing a semiconductor junction comprising amorphous silicon on thesurface of a substrate in an evacuated enclosure comprising a firstenclosure and a second enclosure, a first means for introducing a firstgaseous material comprising silicon and a dopant into said firstenclosure, a second means for introducing a second gaseous materialcomprising silicon and hydrogen into said second enclosure, a means forrestricting the flow of said dopant from said first enclosure into saidsecond enclosure, and a means for transporting said substrate from saidfirst enclosure through said flow-restricting means to said secondenclosure, a first electrode means for applying a first electric fieldto said substrate in said first enclosure and a second electrode meansfor applying a second electric field to said substrate in said secondenclosure, which includes the steps of:introducing said first gaseousmaterial comprising a dopant and said second gaseous materialscomprising silicon and hydrogen at subatmospheric pressures in saidfirst and second enclosures, applying said first electric field by saidfirst electrode means to said substrate in said first enclosures todeposit a doped film on said substrate, transporting by said transportmeans said substrate through said flow restricting means to said secondenclosure, applying said second electric field to said substrate todeposit by glow discharge a film comprising hydrogenated amorphoussilicon onto said doped film while controlling the pressure andrestricting the flow by said flow-restricting means of said first andsecond gaseous materials in said first and second enclosures to deposita film comprising amorphous silicon with a controlled amount of dopantin said second enclosure.
 3. The method of claim 1 further comprisingthe step of moving said substrate relative to said second electric fieldin said second enclosure.
 4. The method of claim 2 further comprisingthe step of moving said substrate relative to said second electric fieldin said second enclosure.
 5. The method of claim 1 in which thesemiconductor property of said film comprising amorphous silicon isenhanced.
 6. The method of claim 1 in which said dopant comprisesphosphorus.
 7. The method of claim 1 in which said dopant comprisesboron.
 8. The method of claim 2 in which said dopant comprisesphosphorus.
 9. The method of claim 2 in which said dopant comprisesboron.